1. Field of the Related Art
The invention relates to a process for the preparation of equilibration products of organosiloxanes by rearrangement of the siloxane bond to a cation exchange resin, the organopolysiloxanes thus obtainable and the use thereof.
2. Description of the Invention
Equilibrations of siloxanes on ion exchange resins are part of the prior art. Among the multiplicity of known systems, the Amberlyst ion exchanger (in particular Amberlyst® 15) is a frequently used catalytic phase.
Thus, DE-A-21 52 270, which is hereby fully incorporated by reference with regard to the present invention, describes a process for the preparation of equilibration products of organosiloxanes by rearrangement of the siloxane bond on a cation exchange resin, organosiloxane used as starting material or an organosiloxane mixture being allowed to flow at a temperature of about 10° C. to about 100° C. through a packing which contains, as cation exchange resin, a macrocrosslinked cation exchange resin containing sulfo groups and having an average pore volume of at least about 0.01 cm3, and the organosiloxanes which have flowed out being isolated.
In addition to the preparation of nonfunctional polydimethylsiloxanes, the possibility for the preparation of copolymeric dimethylsiloxane/poly(methyl)hydrogensiloxanes by equilibration of a mixture consisting of methylhydrogenpolysiloxane, hexamethyldisiloxane and siloxane cycles on the macrocrosslinked ion exchange phase Amberlyst® 15 is described therein.
Copolymeric dimethylsiloxane/poly(methyl)hydrogensiloxanes are, inter alia, valuable starting materials in the preparation of PU stabilizers, in particular for hot flexible foam systems. On the basis of the teaching of DE-A-21 52 270, an attempt was made to prepare a proven stabilizer system by first bringing a mixture consisting of hexamethyldisiloxane, poly(methyl)hydrogensiloxane and siloxane cycles under the action of Amberlyst® 15 as an acidic catalyst at 95° C. into equilibration equilibrium, then subjecting it to a rearrangement reaction with a mixture of allylpolyethers with linkage of SiC bonds to the siloxane backbones under the catalytic action of a platinum metal complex.
However, the polyethersiloxane obtained thereby was in the form of a turbid liquid whose stabilizing activity in the foaming of flexible foam systems is limited in such a way that collapse results when they are used as a stabilizer.